Flake served six terms in the U.S. House of Representatives and has since represented Arizona in the U.S. Senate for the past six years.

In October, Flake announced that he would not seek re-election. A spokesperson for Flake confirmed reports of the senator’s decision to leave politics being linked to the divisive climate created under President Donald Trump.

The two have gone head-to-head since the start of Trump’s presidential campaign.

Flake has been outspoken about the president, which have led to feuds between the two.

The senator published a book, “Conscience of a Conservative: A Rejection of Destructive Politics and a Return to Principle,” expressing discontent with his party for their failure to stand up to Trump in last year’s presidential race.

Despite the senator not seeking re-election when his term ends in January 2019, Flake said in an interview with ABC’s “This Week” in December that a presidential run in 2020 could still be in his future.

“I don’t rule anything out, but it’s not in my plans,” Flake said.

Flake will join former Vice President Joe Biden (2017) and former President Bill Clinton (2007) as recent politicians to take the stage at Harvard’s Class Day ceremonies.

The ceremony will take place on Wednesday, May 23 at the Harvard Law School in Cambridge, Mass.